Presently, delamination of an adhesively bonded structure may be performed by inserting a strip or piece of TEFLON (or like substance) into the bond in an area where the defect is desired, prior to the parts of the structure being adhered. Adhesive is then applied to the parts to be adhered and directly over the TEFLON strips, and the structure is assembled. The surface of the TEFLON is very slick and non-porous, thereby preventing the adhesive from adhering well to the TEFLON. When the adhesive is cured, the area defined by the TEFLON strips becomes a void in the adhesive layer. This void is treated as a defect.
Another method is to introduce contaminants (e.g., mold release agent, wax) into the bond in an area where the defect is desired prior to the parts of the structure being adhered. Upon curing the adhesive, the contaminated area becomes a locally weak, defective section in the bond (in comparison to the rest of the bond). Still another method is to construct the bonded structure, then mechanically drive a wedge into the bond line, forcibly separating the bonded parts.
After the adhesive is cured, the bonded structures are mechanically stressed, and the local defects are monitored for growth (by, e.g., ultrasonic techniques or X-rays).